Inductive plethysmography (IP) is a measurement technology useful for physiological monitoring, especially for ambulatory physiological monitoring. IP sensors can be disposed on monitored subjects, either directly or attached to or incorporated into various kinds of comfortable, unobtrusive garments, for example, in bands, or in partial-shirts, or in shirts, or on partial body suits, or in full body suits, or in caps, and the like. See, e.g., U.S. Pat. No. 6,551,252 B2 issued Apr. 22, 2003. Often, respiration is monitored by combining signals from an IP sensor about the rib cage (RC) and an IP sensor about the abdomen (AB). Coefficients used for combining RC and AB signals in respiration signals can be determined by calibration procedures. See, e.g., U.S. Pat. No. 4,834,109 issued May 30, 1989 and U.S. Pat. No. 6,413,225 B1 issued Jul. 2, 2002. It is also known that differential lung function can be obtained by combining signals from more localized IP sensors overlying the right and left lungs. See, e.g., U.S. Pat. No. 5,159,935 issued Nov. 3, 1992. All four of these cited patent are incorporated herein by reference in their entireties for all purposes.
Further, signals from one or more IP-based sensors about a subject's thorax and/or abdomen can be processed and interpreted to provide, for example, respiratory rates, respiratory volumes, and indications of respiratory events such as coughs and the like. See, e.g., U.S. patent application Ser. No. 10/822,260 filed Apr. 9, 2004 (which is incorporated herein by reference in its entirety for all purposes). Signals from one or more IP-based sensors about a subject's thorax at the level of the xiphoid process can be processed and interpreted to provide, for example, cardiac stroke volumes, and the like. See, e.g., U.S. Pat. No. 6,783,498 B2 issued Aug. 31, 2004 (which is incorporated herein by reference in its entirety for all purposes).
Generally, an IP sensor includes a conductive element that is placed about, usually enclosing, a portion of the body to be monitored. As the size of the enclosed body portion changes, for example, because of respirations and/or cardiac contractions, electrical properties of the conductive element changes. Sensor electronics measures these change and produces output signals, which can be processed into data reflective of areas, circumferences, diameters, and similar geometric measures, of the monitored body part enclosed body cross section. The resulting area, circumference, diameter, and similar information is useful for physiological monitoring applications.
Since it is important that the conductive element, usually a wire, move with the monitored body part, this element is usually not directly mounted but it supported by an elastic material which is in contact with the monitored body part. The supporting elastic material has usually been a knitted, woven, crocheted, or braided textile on which the sensor wire is mounted and affixed in a wavy, sinuous, or approximately sinusoidal pattern. See, e.g., U.S. Pat. No. 6,341,504 B1 issued Jan. 29, 2002 (which is incorporated herein by reference in its entirety for all purposes).
However, these known IP sensors have generally been limited to performing only IP sensor functions. Furthermore, their sensor functions has lacked desirable sensitivity, performance, and other important sensor properties.
Citation or identification of any reference in this section or any section of this application shall not be construed that such reference is available as prior art to the present invention.